Such circuits are for example used in the measuring and selecting units of measuring arrangements, the measuring and selecting units of which are connected by means of a cable one with the other and with a central unit from which they can be individually selected and activated and to which, at least in the activated state, they can deliver information data, such as for example measurement results.
Such measuring arrangements are for example described in the published German patent application Ser. No. 30 25 837. In order to select and to activate an individual measuring or selecting unit a respective address signal in the form of coded electrical pulses is emitted from the central unit on a respective core of the cable to all measuring and/or selecting units of the system. Each measuring and selecting unit of the system comprises an addressable circuit with an address memory which stores an address characterizing the respective measuring or selecting unit, and an address recognition circuit which compares the stored address with the addresses transmitted from the central unit. Only the address recognition circuit of the measuring or selecting unit the stored address of which is identical with the address transmitted from the central unit generates a control signal which is used for further purposes as, for example, for closing or opening a switch, for enabling or disabling gate circuits and so on.
In such known measuring arrangements it is further required to transmit to the measuring and selecting units at least one further kind of signal which pocesses a function different from the address signal but likewise has the form of electrical pulses. In the measuring arrangement described in the abovenamed published German patent application, the further kind of signals are setting pulses which must be fed to the address recognition circuits of the addressable circuit arrangements at least at the start of each interrogation cycle in order to set these address recognition circuits into a state of readiness, starting from which they are in a position of comparing addresses sent from the central unit with the individual address stored in their circuit arrangement and of generating a control signal on co-incidence. In the named German patent application a logic "1" is then entered into the first stage of a shift register with the aid of this control signal, which logic "1" is then in the further course shifted from stage to stage through the shift register. Instead thereof, however, an otherwise opened switch can be closed transiently or a normally closed switch can be opened briefly or any kind of similar function can be initiated by means of the control signal.
From the published German patent application Ser. No. 30 25 837, it is known to feed the address signal pulses and the setting signal pulses from the central unit to two separate inputs of the addressable circuit arrangements. This has the disadvantage that an individual signal transmission path, for example an individual cable core, must be provided for each further kind of signal which is to be fed to the addressable circuit arrangements in addition to the address signal.
In order to overcome the need of providing as many signal lines as different kinds of signals are to be transmitted from the central unit to the measuring and selecting units it is possible to transmit all the different kinds of signals on one and the same line or core of the cable and, at each measuring and selecting unit, to feed them to one and the same unit input.
For distinguishing the signal pulses of the different kinds from one another the pulses of each kind of signal have a specific length or width in time which is different from the widths of the signal pulses of all other kinds of signals. From the input of each measuring and/or selecting unit, to which all these different signal pulses having different widths are fed, they are forwarded to a pulse width discriminating circuit which has as many outputs as different kinds of signals are to be discriminated.
For each output of the pulse width discriminating circuit a specific lower and a specific upper limit are provided and the discriminating circuit generates upon receipt of a signal pulse an indication signal at a given output only if the width of the respective signal pulse is greater than the corresponding lower limit and less than the corresponding upper limit.
It is an objective of the invention to provide a pulse width discriminating circuit which is able to determine exactly whether the width of at least one kind of signal pulses is greater than the respective lower limit and less than the respective upper limit by using only a very small number of simple and reliable circuitry units the number of which is to be enhanced only slightly if for each of several different kinds of signal pulses a respective indication signal is to be generated at a respective output.